Email Deliverability: A Detailed Look at the Best-Performing Tools

Inka Wibowo

Inka Wibowo

Latest Update: 7 Jan 2019

Email deliverability can really make or break an email marketing campaign. Most marketers know the theory behind boosting deliverability rates – maintaining clean lists, keeping subscribers engaged, building a good sender reputation, and so on. But many also know from experience that you can do everything by the book, and still have your emails mysteriously disappear after being sent.

Based on our email deliverability tests, we’ve confirmed what many marketers have long suspected – different newsletter services do have different deliverability rates. And the differences, in some cases, are quite startling.

As a result, we’ve decided to share our results, and have committed to performing regular tests to make sure our results are always up to date. We’ll continue to add them to this page with each round of tests.

Because we believe deliverability should be an important factor when deciding on which email tool is right for your business, we’ve also now added this as a criterion to each of our reviews.

Where exactly are emails landing?

It’s no surprise that there’s a direct correlation between low deliverability rates, and high rates of email flagged as spam. Below is a breakdown of where exactly emails ended up (whether it was the main inbox, a secondary tab, spam folder, or if it went missing), in each test round we’ve completed.

Inbox placement rates August 2017

Inbox placement rates March 2018

Inbox placement rates January 2019

Based on these results, we can start to see some general trends:

Benchmark, SendinBlue, AWeber and Mailify tend to have a higher proportion of emails that get filtered to spam. On the other hand, the same emails sent through ActiveCampaign and Constant Contact were much less likely to be marked as spam

Historically, MailChimp emails had a much higher chance of ending up in a secondary tab (instead of the main inbox), although this is changing. We explore this in more detail in the Google Primary Inbox vs Promotions Tab section below

Deliverability rates by Internet Service Provider (ISP)

Thanks to Glockapps.com, we were able to see just how well each newsletter service performed in getting delivered to the four main ISPs – Gmail, Microsoft (Outlook and Hotmail), Yahoo and AOL. Based on our results, you can see that certain ISPs definitely look more favorably upon some tools than on others.

Deliverability to Gmail

Provider

Deliverability % Aug 2017

Deliverability % Mar 2018

Deliverability % Jan 2019

ActiveCampaign

100

100

100

AWeber

100

100

100

Benchmark

50

100

0

Constant Contact

50

100

100

ConvertKit

100

100

100

Drip

100

100

Not tested

GetResponse

50

100

100

MailChimp

100

100

100

MailerLite

100

100

100

Mailify

Not tested

Not tested

80

SendinBlue

100

100

100

Deliverability to Microsoft (Outlook and Hotmail)

Provider

Deliverability % Aug 2017

Deliverability % Mar 2018

Deliverability % Jan 2019

ActiveCampaign

50

100

100

AWeber

0

19

0

Benchmark

0

0

0

Constant Contact

84.4

100

100

ConvertKit

84.4

83

86

Drip

0

100

Not tested

GetResponse

50

11

20

MailChimp

50

40

62

MailerLite

0

100

100

Mailify

Not tested

Not tested

35

SendinBlue

50

13

0

Deliverability to Yahoo

Provider

Deliverability % Aug 2017

Deliverability % Mar 2018

Deliverability % Jan 2019

ActiveCampaign

100

100

100

AWeber

100

100

100

Benchmark

100

100

100

Constant Contact

100

100

100

ConvertKit

100

100

97.5

Drip

100

100

Not tested

GetResponse

100

97.5

100

MailChimp

100

100

100

MailerLite

100

100

100

Mailify

Not tested

Not tested

80

SendinBlue

100

100

97.5

Deliverability to AOL

Provider

Deliverability % Aug 2017

Deliverability % Mar 2018

Deliverability % Jan 2019

ActiveCampaign

7.1

100

100

AWeber

100

100

80

Benchmark

0

80

100

Constant Contact

92.9

100

100

ConvertKit

100

100

100

Drip

100

100

Not tested

Get Response

85.7

100

100

MailChimp

100

100

100

MailerLite

100

100

100

Mailify

Not tested

Not tested

74.3

SendinBlue

85.7

100

100

What does this mean? Well, if you have a good sense of who your subscribers’ email providers are (in an ideal world, that would be Yahoo!), you might consider choosing a newsletter service based on this. Of course, that’s often difficult to know. Plus, as our results show, deliverability to ISPs can change over time.

It’s perhaps more useful to just keep an eye out for any red flags. For example, Microsoft clearly apply more stringent filtering to inbound emails, and some newsletter services – such as Benchmark and AWeber – seem to really struggle to get through to their inboxes. So if your deliverability rates are inexplicably low, this may very well be the reason why.

Gmail Promotions Tab vs Primary Inbox

While the newsletter services were generally able to deliver to Gmail mailboxes just fine, not all ended up in the Primary tab. Perhaps this isn’t a surprise to anyone who’s used Mailchimp, but our first two rounds of tests found that MailChimp had a much higher chance of getting relegated to a Promotions tab – even with emails that wouldn’t normally be considered ‘promotional’.

In the latest round, however, this changed – only 60% of MailChimp’s emails to Gmail ended up in Promotions (instead of 100%). Other previously-safe providers also had a much higher chance of landing in Promotions (MailerLite, SendinBlue, AWeber, ConvertKit). ActiveCampaign, GetResponse and Constant Contact were the only providers who ended up in Gmail’s main inbox each time.

Proportion of Gmail-delivered emails that ended up in Promotions tab

Provider

Aug 2017 %

Mar 2018 %

Jan 2019 %

ActiveCampaign

0

0

0

AWeber

0

0

60

Benchmark

20

0

0 (note – 100% went to spam)

Constant Contact

11.4

0

0

ConvertKit

0

0

60

Drip

0

0

Not tested

GetResponse

0

0

0

MailChimp

100

100

60

MailerLite

0

0

60

Mailify

Not tested

Not tested

40 (note – 20% went to spam)

SendinBlue

22.9

0

60

There’s no telling why some providers get sorted to Promotions and others don’t, as Google’s complex sorting algorithm is kept tightly under wraps. Ending up in Promotions is less than ideal, as your email is likely to get lost in the flood of emails that often make their way to that tab. Then again, if your email really is promotional and your subscribers are used to accessing emails from that tab, it may not be a problem.

Our email deliverability test methodology

Using Glockapps.com, we ran our first round of testing in August 2017. This round comprised 5 separate tests conducted over several weeks. We wanted to make sure all conditions were equal, so in each test, we:

Set up a sender subdomain for each of the tested tools, plus SPF and DKIM records where available

Used the same email (always text-based, sometimes with links, and sometimes without)

Sent to the same seed list (representing 28 ISPs worldwide, including Gmail, Outlook, AOL and Yahoo; weighted according to the popularity of the email service)

We repeated this very same test round in March 2018, and in January 2019.

Why do some tools perform so much better than others?

We’d love to know what the top performers' secret is – and we’re sure some of the other tools do too! What we do know is that the ISPs often have the last say on whether an email lands in an inbox. This means that they have to trust the mail server sending that email; in our case, that means the server used by the newsletter service.

If that same server also happens to be sending out emails for other clients that are considered ‘spammy’, deliverability of your own emails could suffer. Newsletter services therefore make it a priority to maintain their server’s reputation. But some are clearly doing a better job of this than others.

What does this mean for me?

When choosing a newsletter service, there are obviously many factors to consider – price, features, usability, and so on. But with these results, we’ve hopefully made it easy for you to shortlist (or discard) a few based on potential deliverability.

Note that we said ‘potential’ – there’s simply no way of knowing for sure how deliverability will play out for each business. Our results can give you a general idea of what you can expect, and what things to look out for, but your own experience may be very different. If so, we’d certainly like to hear about it!

Does this mean marketers are completely powerless when it comes to the success of their campaigns? Not at all. If anything, these results really drive home the importance of understanding your subscribers – for example, how they engage with emails, and what content they’re likely to be interested in – and to tailor your email campaigns to their preferences. That way, even if you don’t have complete control over who gets your email, you’ll at least maximize their effectiveness with those who do.